Water-soluble polymer invert emulsions (water-in-oil) are widely used in many domains for the thickening and flocculating properties thereof. This particular form has the advantage of being able to provide, in concentrated liquid form, high molecular weight polymers. The emulsion, however, should ideally be inverted in more or less concentrated form prior to the use of the polymer, mixing water with the invert emulsion in such a way as to obtain a continuous aqueous phase wherein the polymer is located.
The invert emulsions, dehydrated or not, of acrylamide-based water-soluble polymers are useful in particular in enhanced oil recovery (RAP or EOR for Enhanced Oil Recovery) and more particularly in off-shore operations. An aqueous polymeric solution is typically prepared on the platform. Generally, the emulsion is inverted by means of the addition of water and then mixed within a mixer, for example a static mixer, in order to produce a mother solution with a concentration of between 2,000 and 20,000 ppm. The mother solution itself is diluted downstream with water or brine in order to produce the polymeric solution injected into the subterranean formation, wherein the polymer concentration is typically in the range of 100 to 2,500 ppm.
It is essential that the emulsion be well inverted because in being well inverted it will provide the polymer solution with optimum viscosity and injectivity, the polymer being completely available and homogeneously distributed in order to thicken the aqueous medium. When the emulsion is not properly inverted part of the polymer does not perform the thickening role thereof, resulting in a loss of efficiency and injectivity of the solution prepared from the emulsion.
Likewise, water-soluble polymers in powder form are particularly useful in enhanced oil recovery especially in on-shore operations. The powders are prepared in the form of a solution by means of the dissolving of the powder in a more or less concentrated solution. Generally, the powder is dissolved by virtue of a dissolving apparatus, such as the PSU (Polymer Slicing Unit) described in WO2011/1076863, to a mother solution concentration ranging between 2,000 and 20,000 ppm, said mother solution being deposited in maturing tanks under agitation, then diluted downstream with water to produce said diluted polymeric solution wherein the polymer concentration is typically of the order of 100-2500 ppm.
It is also essential that the powder be well dissolved and the polymer well solubilized in water or brine.
Subsequently, the expression “effective polymer solution preparation” denotes the implementation thereof under conditions that make it possible to obtain optimum solution viscosity. The optimum solution viscosity is the viscosity attained when 100% of the water-soluble polymer is dissolved in water or brine. This optimum viscosity is in practice between 1 and 200 mPa·s (between 1 and 200 cps) (measured at 20° C. using a Brookfield rheometer with a UL module).
The term ‘use region’, refers to the most downstream location theoretically accessible to the method wherein the polymeric aqueous solution is used. For example, in the case of an EOR Off-shore operation, this location is at the swivel in the subterranean formation located at the bottom of the sea or ocean.
For this, it is known to occasionally take a sample of the polymeric aqueous solution in order to verify the viscosity thereof in relation to the viscosity of a solution prepared under optimal laboratory conditions.
However, in the case where the diluted solution is not accessible or not easily accessible, it is sometimes impossible to collect a sample of the solution. This is typically the case at the wellhead when it is at the bottom of the sea or ocean in an off-shore operation, wherein the difficulty is technical. This is also the case when the mother solution is for example prepared within a centralized dissolving station and then transported through long pipelines to dilution sub-stations and finally to the injection wells. The wellhead can then be located within a risk zone (military zone) or within a restricted access protected area in an onshore operation, where the solution preparation location is situated within an accessible area. The problem may arise in many other cases.